The present invention relates to a downhole seismic energy source which electromagnetically generates seismic waves for geophysical exploration.
The use of seismic sources on the surface is common in geophysical exploration. With the developments in vertical seismic profiling (VSP) and cross borehole technology, the need for a downhole source has increased. A downhole source makes VSP and cross borehole measurement practical, however, downhole seismic sources are uncommon, have limited depth and frequency range, and typically are either low power or destructive.
Due to design constraints of placing a source down a wellbore, at present there is no adequate downhole seismic source. Dimensions of a downhole source are limited by the size of the wellbore. Typical downhole tools must be limited to about 12.5 cm (.about.5 inches) in diameter. The source must also be able to withstand the temperature, pressure, and fluids encountered at depths of 6000 meters (.about.20,000 ft) beneath the surface. Adequate power must be transmitted from the surface to the source or the source must carry its own power supply. The source must then generate forces of between 1,000 and 18,000 newtons thereby creating seismic waves which may be detected in another well or from the surface at desired offsets from the well. The downhole source should be controllable and capable of variation in frequencies generated. Most importantly, the downhole source must do all these things without damaging the well.